REVERSION RATE BUT NOT EXCISION RATE IS REDUCED IN BZ-M13 CS17

The variegated phenotype of a given transposable element (TE) insertio n mutation in maize (Zea mays L.) reflects the timing and frequency of excision of the TE from its host gene. Here we describe a ''change-in state'' (CS) derivative of bz-m13, termed CS17 Structural analyses in dicate that both alleles of the bronze1 (bz1) gene contain an identica l 2.24 kb defective Suppressor-mutator (dSpm) insertion in the Bz-McC2 allele, and that CS17 differs from bz-m13 only in a 5 bp deletion imm ediately 3' of the insertion. In the presence of Spm, aleurone reverta nt sector size is reduced in CS17 as compared with bz-m13. However, mo lecular assays of somatic excision yield similar results for these two alleles. Also, germinal excision rates are similar but germinal rever sion is reduced in CS17 as compared with bz-m13. This illustrates that in cases where TE excision can give rise to both stable gene function (reversion) or non-function (recessive or null phenotype), the size o f a revertant sector or number of germinal revertants is a function of both the frequency and timing of excision and the probability that a given excision event will be a reversion.